1. Field of the Invention
This invention relates to a new method for preparation of 2-phenylsemicarbazides.
2. Description of the Prior Art
There are relatively few examples in the prior art of groups useful for protecting the NH.sub.2 group of a (substituted)phenylhydrazine while a carbamoylation is carried out on the remaining NH group adjacent to the (substituted)phenyl. In all the known examples, the NH.sub.2 group is protected by converting the phenylhydrazine into the corresponding benzaldehyde phenylhydrazone prior to carbamoylation. Historically the benzaldehyde protective group has been removed by addition of equimolar amounts of 2,4-dinitrophenylhydrazine or more recently by refluxing in dilute aqueous hydrochloric acid and removing benzaldehyde azeotropically with steam as it is formed. Applicant has now discovered an alternate synthesis that avoids the use and recovery of benzaldehyde, a relatively expensive and toxic intermediate protective group.
No prior art has been found by applicant which describes the new multi-step process of the present invention.
U.S. Pat. Nos. 3,585,200 and 3,755,443 disclose the reaction of certain 2-substituted-.DELTA..sup.2 -1,3,4-oxadiazolin-5-ones with alkylene diamines to form 4,4'-alkylene bis(1-acylsemicarbazides), which may then be hydrolyzed to the diacid salts by heating with aqueous mineral acids to produce materials suitable for use as blowing agents in polymers.